The long term goal of this application is to improve the outcome of seizure surgery by better presurgical localization of medically refractory epilepsy using a combination of neuroimaging techniques including magnetic resonance imaging (MRI), 1H and 31P MR spectroscopic imaging (MRSI), and 18F-PET. These techniques will be directed at three groups with medically refractory epilepsy who are being evaluated for seizure surgery (numbers for 5 years): 1)patients with medial temporal lobe epilepsy in whom MRI is non-concordant i.e., MRI shows no abnormality, or an abnormality contralateral to the EEG-defined seizure focus (NC-mTLE, n=75), 2) patients with non-lesional neocortical epilepsy (NE, n=100), and 3) children with Infantile Spasms (IS, n=100). NC-mTLE and NE patients frequently require invasive EEG recording, have less than a 50 percent probability of becoming seizure free with surgery, and are often not considered for surgery. Post-operative surgical outcome will be analyzed in relation to the pre-operative neuroimaging findings. Hypotheses: 1) NC-mTLE -Patients with medically refractory mTLE without MRI concordance, who have 1H and 31P MRSI measures concordant with the EEG localization (i.e., lobe and side), will have a significantly better post surgical outcome than patients without MRSI concordance. 2a) NE - NE patients without lesions on MRI, will have 1H and 31P MRSI concordant with the EEG localization (i.e., lobe and side), and this concordance will be greater than that provided by 18FDG-PET. 2b) NE - NE patients, who have 1H and 31P MRSI measures concordant with the EEG localization will have a significantly better post surgical outcome than patients without MRSI concordance. 3a) IS - Children with medically refractory Infantile Spasms will have 1H and 31P MRSI concordant with the seizure focus determined by a combination of two or more studies (VET, 18FDG-PET, and/or MRI) and this concordance will be greater than that provided by MRI or 18FDG-PET. 3b) IS - IS children, who have 1H and 31P MRSI concordant with the localization provided by the other clinical and imaging studies will have a significantly better post surgical outcome than patients without such concordance. These studies are expected to lead to improved surgical outcome, and to reduce unnecessary surgery, in patients with intractable epilepsy.